This invention relates to ski boots. In particular, it relates to a boot for enhancing the safety of skiing.
The leg of a skier may be seriously injured due to unexpected forces and pressures applied to the leg, which can include the thigh, knee, calf, lower leg, ankle or foot. In particular, a skier's knee may be seriously injured by a forward directed force on the back of the lower leg when the thigh and foot are in a fixed relationship. In some skiing conditions, knee injury arises from forces which occur at the leg-boot interface while no significant distractional or rotational forces occur at the boot-ski interface.
Alpine, or downhill snow skiing currently has an injury rate of 2 to 3 per 1,000 skier-days. This translates to approximately 500,000 injuries requiring the services of "Ski Patrol" per year in the United States.
The bone of the thigh, namely, the femur, is joined to the major bone of the lower leg, namely, the tibia, by several ligaments and muscles spanning the knee joint. One of these ligaments, the Anterior Cruciate Ligament (ACL), prevents excessive forward translation of the tibia relative to the femur. Forces greater than the ultimate strength of the ACL result in rupture of this ligament. ACL injury incidence has increased about 500% while other ski injuries have decreased to less than about 50% of 1970 levels due to improvements in safety equipment. Higher, stiffer and forward leaned boots are believed to have shifted the site of injury to the knee.
Previously, ski safety devices were located at the bindings affixing the boot to the ski. The boot was released from the ski when excessive upward forces were present at the boot heel or when torquing forces were present at the boot toe. These devices have successfully lessened ankle and tibia injury incidence.
A few toe piece bindings also release in response to an upward force in an effort to protect the knee. However, these upward forces may be negated by the weight of the skier transmitted through the boot to the ski. This renders the release mechanism ineffective despite injurious forces acting at the knee. Thus, because of their design and location, ski bindings may not be able to release in response to injurious forces directed at the skier's leg that are not detected at the ski binding. For example, as depicted in FIG. 2, in a situation when a skier is landing from a jump or descending from a bump, the rear portion of the ski first contacts the snow covered ground. The weight of the skier acting on the ski causes a clockwise rotation of the ski and the boot attached to the ski also rotates forward. This causes pressure applied to the calf by the rear of the leg element of the boot. The thigh and the remainder of the skier's body are relatively fixed by inertia. The resulting force directed against the skier's calf may be great enough to exceed the strength of the ACL and cause its rupture.
The ski bindings do not release in this situation because (1) the downward force of the skier's weight negates any upward forces which otherwise might cause release; and (2) the injurious forces directed against the skier's calf are oriented in a direction parallel to the long axis of the ski. Known ski bindings respond only to forces on the ski in a direction perpendicular to the long axis of the ski.
A system for protecting skiers against the rising incidence of ACL knee and leg injuries would be of considerable value.